Matt Springer has been giving presentations around San Francisco about home earthquake preparedness since 2008 (for more information about the presentation, go to his earthquake preparedness website). This blog is devoted to posts ranging from technical "how-to" articles to more philosophical "should-you" topics. New articles will be posted at most about once a month, so people who subscribe won't be subjected to lots of e-mail.

Thursday, October 16, 2014

Can you use a portable camping water filter to safely drink tap water after an earthquake in case your emergency water is gone? (Spoiler alert: the answer is no.)

It’s about a week after a major earthquake, and your commercial emergency water bottles, regardless of the date stamped on the side, are all used up.  There is no running water from your faucets, or there is water but your utilities company hasn’t yet managed to confirm that it is safe to drink, and the government is overwhelmed trying to bring in water supplies to a large affected area.  Your water heater and UPPER toilet tank are emptied out.  And even if you are in San Francisco, the potable water hydrants are defunct and haven’t been recertified yet.  What now?

Well, there are the long-known last resorts of using water purification tablets, boiling, diluted bleach, etc.  But there’s a new kid on the block, growing in popularity over the last several years: the personal water filter.

I may be a bit behind the curve on this one, but I’ve only recently become aware of several types of portable, lightweight, hollow fiber membrane water filters that you can use to drink water directly from potentially unsafe ponds and streams.  These filters, the best-known of which are the LifeStraw from Vestergaard and the Sawyer MINI from Sawyer, let you suck water through them directly from the questionable source and drink it.  Last month, a reader inquired as to why they weren’t on my list of emergency supplies, and I decided to investigate.

I was pretty impressed by these devices, at least regarding use in the undisturbed wilderness.  I know that putting one end of a cylinder into a pond with Cryptosporidium and Giardia (which are as bad as they sound), or MONSTER PARASITES THAT EAT YOUR BRAIN (they are probably out there somewhere), and sucking water through the cylinder and DRINKING IT might sound concerning.  However, these hollow fiber filters are quite good at keeping out the bad stuff while letting the water in, and still allowing water to flow quickly enough that you can drink it in real time.  Time Magazine gave LifeStraw their award for Best Invention of 2005.  The LifeStraw and Sawyer filters use FDA-compliant materials and yield water that the companies report to meet US EPA drinking water standards and World Health Organization “highly protective” category standard of safe water.  Hang on, though, we’ll look more closely at these health claims in a minute.

Hollow fiber filter (from Sawyer website)
First, let’s look at how they work (humor me, I'm a scientist).  Inside the cylinders are bundles of tiny hollow fibers with tinier holes in their walls.  The fibers are bent so that both ends are densely packed toward the drinking end of the cylinder, and the middles are facing the water source so that water has to get from outside the fiber to inside the fiber before it can come out the drinking end (or perhaps the other direction, descriptions vary).  The size of the tiny pores determines what gets filtered out.  Because the fibers are so small and there are so many of them, there’s a huge surface area for filtration, and the water flows through the filter fast enough to have a satisfying drink.

They do have a finite lifespan of use, however, with LifeStraw filtering up to 264 gallons (that’s 1000 liters, so it really is a round number) and Sawyer Mini filtering up to 100,000 gallons.  They also store indefinitely.  For a while, LifeStraws were given a storage life of 5 years but this was later revised to indefinite.

Sawyer MINI
They also come in different forms that have varying advantages depending on what you want to do.  The basic LifeStraw is about 9 inches long and you can see pictures on the web of people lying down to get their faces within 9 inches of the surface of a pond; perhaps not ideal on a muddy shore or one infested with scorpions, but probably not a problem if you have scooped up a bottle of water from a suspicious pond and are drinking that through the filter.  The Sawyer MINI is even shorter, 5 inches including its tips, so it fits better into backpacks, and it has a real straw that attaches to the end that effectively extends it to 12 inches.  They both have the ability to be attached to standard water bottles and you can get them with their own bottles and bags.  Here’s where Sawyer has a nice feature; while they both have bottles that incorporate the basic filter cartridges, these take up space, and the Sawyer has a bag that screws onto the bottom of the cartridge but can be rolled up when empty, taking up practically no space.

Most importantly, what about health?

LifeStraw filters through 0.2 micron pores.  (A micron, or micrometer, is one one-thousandth of a millimeter; the typical bacteria living inside your gut is about 2 microns long and about 0.5 micron wide.)  LifeStraw claims that this yields good drinking water, EPA compliant, etc.  Sawyer filters to 0.1 microns or 0.02 microns depending on the version.  Sawyer states that the 0.1 micron filter takes out 99.99999% of bacteria and 99.9999% of protozoans (like Cryptosporidium and Giardia), but does not remove viruses due to their smaller size.  Sawyer thus considers this filter safe for travel around the North American wilderness but not for third world countries, in which viruses like hepatitis A in the water supply is a big concern.  (Human-infecting viruses do not persist in the wild; their presence in the water is typically from contamination with human waste/sewage.)  They claim that the 0.02 micron filter takes out 99.9997% of viruses and that this exceeds EPA recommendations, although they point out that the 0.02 micron filter takes a longer time to pass water, and suggest that you use the 0.02 micron filter if you will go to a third world country.  Unfortunately, the 0.02 micron Sawyer filter system does not appear to be available in the small portable size, and is much more expensive.

(But wait, LifeStraw makes a big deal about its filters with their 0.2 micron filtration being used in developing countries; they have been partnering with various charities to give free filters to people in various African countries, Haiti after the recent typhoon, etc.; so this contradiction is confusing.)

It’s worth noting that these pore size figures are not the average pore size, with some pores being smaller and some larger; they are absolute pore sizes, so no pore should be larger than the number given.  One more important point is that these are physical filters; they don’t include resins or activated charcoal so they don’t take out chemicals or bad tastes like commercial kitchen water filters do (for example, Brita).  So if you use these to drink from germ-laden disgusting water, you’ll ingest germ-free disgusting water.  And remember, no filter can let you drink saltwater.

Ok, so what about health AFTER AN EARTHQUAKE?

Still, what concerns us most in this article is: what about health in a modern city after an earthquake?  After all, it’s one thing to wander around in the Rocky Mountains drinking from beautiful streams, but what will our water supply look like after an earthquake has potentially compromised our water pipes?  Well, I checked with emergency planners and water quality engineers at the San Francisco Public Utilities Commission, and I have disappointing (not to mention rather disturbing) news from Water Quality Division Engineering Manager Manouchehr Boozarpour.  Normally, our potable water pipes carry potable water, and our sewage pipes contain sewage, and never the twain shall meet... unless both kinds of pipes crack during an earthquake, in which case cross contamination is likely.  Yep, THAT’s what they mean when they say you need to purify tap water after an earthquake, and because the sewage potentially introduces viruses, which are not removed by the 0.2 and 0.1 micron portable filters, the water from your post-quake tap is likely to be more dangerous than the water in the mountain pond.

So, unfortunately, a LifeStraw or Sawyer individual filter tube does NOT offer sufficient protection to drink potentially contaminated tap water after an earthquake in a city.  The options that I can see to decontaminate suspicious tap water are to either pack one of these small filter tubes in your portable emergency kit but to also have water purification tablets packed to treat the water before you suck it through the filter, or to purchase one of the larger systems that would be intended for home use in the aftermath of a major quake but would be more difficult to take with you if you had to leave.   These kits consist either of Sawyer’s 0.02 micron filter that theoretically removes the viruses, but is slow and requires a large pumping mechanism; or a system that includes both a filter and a chemical water treatment step designed to inactive viruses like the Sweetwater purification system.  Note that chemical purification alone does not guarantee killing of Cryptosporidium and Giardia.  Boiling is great, but you can’t assume you’ll have the necessary heating source to do it, and flame is never a good idea around potential gas leaks.

Purification systems that remove or inactivate viruses
But guess what, even making your water non-infectious doesn’t mean it is safe.  If the ground in your local area, or wherever the pipes are buried, has high levels of industrial pollutant chemicals, then these can also get into the water supply after an earthquake.  I would not count on Brita water filters to solve that potential problem, and boiling that water won't make a difference.  Many regions do not have this problem, but some do.  For this reason, I think the best advice I can give here is to be prepared and able to remove/inactivate microorganisms including viruses, BUT to drink only your stored emergency water until you have heard from your own local authorities about what problems are affecting your own local water supply.  It follows, then, that none of these purification systems get you off the hook from having to store emergency water.

The Centers for Disease Control has a very useful and detailed document about emergency water purification that is worth reading.  (Just don’t be surprised to see their comment that you should observe printed expiration dates on commercially bottled water, which contradicts the FDA’s advice about which I wrote last year that you can ignore those dates.  Remember that the FDA is the agency charged with regulating safety of bottled water, so I am comfortable giving priority to their advice on the matter.)  One of the links on that page takes you to another useful guide about relative effectiveness of different chemical purification methods.

Bottom line: I still advise keeping sufficient emergency water supplies handy so that you don’t have to purify tap water in the first place.  Still, we can’t know that a more extended water shortage won’t develop (remember, the Red Cross is recommending TWO weeks of emergency supplies now), so having the ability to remove microorganisms including viruses may still come in handy if the local authorities tell you that you can drink the water if it's been boiled.

I had never realized how much we take our water faucet for granted!

>>back to blog


  1. What about if you aren't on city water to begin with? I have a well, and septic system, pipes are more than 100ft apart. I'm in Alaska on the outskirts of one of the larger cities. I realize there could still be sediments and such loose in the ground water, but could some filter or combination thereof work in this instance?

  2. Based on what I have read, I imagine that this would be more like a typical wilderness camping situation, in which viruses aren't a problem so the filters that don't remove viruses are sufficient. Whether or not you have ground chemical pollution there is hard for me to know; you probably have a better idea. If you don't envision ground chemicals being a problem, then it sounds like these .1 and .2 micron filters should be a reasonable post-quake solution.

  3. I have slightly updated the text of the article to reflect this.

  4. The handheld UV water purifiers, like SteriPEN, have been around for a while. They kill viruses, and you can get a pre-filter with them to get rid of cloudiness or sediment. See for more information. Available in various models for under $100 at places like REI.

    1. Thank you for this useful information. This sounds like a reasonable alternative to the chemical purification steps (although I have not checked into it any further than the information on the SteriPEN website). They do have the disadvantage of needing batteries, but that is ok assuming that you have enough batteries stored and they are still fresh (see my recent article on choosing the right batteries for your emergency supplies; I note that the SteriPEN website suggests lithium batteries over alkaline batteries just like I did). I should point out, however, that the chemical ground contamination could still be an issue if pipes are damaged in an earthquake, and none of the filters, chemical treatments, boiling, or UV treatments would solve that problem. To the best of my knowledge, ground chemical contamination frequently is not a problem, and if the authorities tell you to boil water before drinking it, the SteriPEN sounds like a good alternative. I still suggest having stored drinking water so that until you hear that your local water will be ok if boiled (and if you hear that it won't be ok, due to chemical contamination), you'll still have water to drink. All of these other treatments should be considered as the next layer of preparedness in case you run out of your primary emergency water.

  5. Note to readers: this article has been attracting many attempted comments that are merely disguised advertisements. Unlike the previous comment, which mentioned SteriPEN as a useful contribution to the discussion, most of these submitted comments have been simple "water purification is a good idea"-style comments that then give a URL for a company or product. I have not been allowing these comments through the moderation stage. If someone feels that their comment is being unfairly blocked, please e-mail me.

  6. the lifesaver bottle can be very effective in such situations mentioned above, with a filter power of 0.015 microns. a few other filters would come in hardy too in such situations read more at

    1. Relevant to my disclaimer above, I have validated the existence of this product, and the website listed above appears legitimate, with reviews of similar products.

  7. I liked both of your posts about cleaning water for emergencies. I have been reading Ted Koppel's book Lights Out and it has got me to start putting together plans.I also think that depending on the emergency you may have to leave your home or area and hike it out and having a portable method of cleaning water when you do come across sources is good idea too besides having water stored at home. I live in Washington State and when the 9.0 hits I think I may have to leave the area since it will take forever to get infrastructure repaired. I found a great portable unit that comes out next month but very pricey, I think it will be about $350. I need more info on it thou. But it takes out viruses and when sanitation is bad this could be very valuable for on the go. Here is their video and I am not affiliated with them at all. Just looking for best solutions with all this. Thanks for the tip on boiling the water and adding bleach : )

    1. This is another case where the product mentioned is legit and interesting. The YouTube video is about the MSR Guardian water purification system, which is from the maker of the Sweetwater system mentioned above. It looks interesting in that apparently the hollow fiber filter excludes viruses as well as the larger particles, so you shouldn't have to use a chemical-based sterilizer, although I haven't yet found a pore size for it. It is indeed rather pricey but could be worth it for home use, and is portable although it does take up more space than the simple Lifestraw-style solutions. Their video did not mention a chemical-removing core like some of their other products have, so I'm not sure how it does with ground chemical contamination. I still wonder how this product deals with the taste of donkey pee in the water (to use the example in their video)!

  8. hi, matt. thanks for the info! i bought a sawyer mini and it's going back tomorrow!

    what are your thoughts on the Berkey filter systems? i purchased one for daily use in our home, and it said it removes basically everything (including chemicals). it isn't super portable though, which is why i got a sawyer mini. but i'm wondering if it's worth toting around in an emergency if it removes the most contaminates?

    1. Thanks for your note; I'm a bit swamped at the moment but will look into it and post my thoughts when I have a chance; might be a week though. Just didn't want you to think your comment was being ignored.

    2. I just looked up the Berkey systems on the web. Well, from their description, it sounds pretty good in terms of specifications. The large systems are clearly not the best for portability but if you were already looking at a non-portable system for home use in the aftermath of a disaster, there isn't much difference there. I was wondering however why their comparisons to their competitors omitted Sawyer and LifeStraw and instead used more standard home filtration systems. I also noted that their explanation about what happens when you drink hypotonic water sounded a bit sketchy to me from my background in the biological sciences. But if the filters do indeed perform as they say they do, they are probably good. I'm afraid that's the limit to what I could conclude without considerably more research.

    3. i guess if the portable Sawyer and Lifestraw are not good for after an earthquake within a city environment, it's better to have a bulky system that does filter out what's needed. the compartments also nestle within themselves when not holding water, which makes it more portable if really needed.

      i had never heard of Sawyer or Lifestraw before putting together an emergency kit, so it's ironic that they aren't sufficient protection in that situation!

      not sure what your note on hypotonic water is... (i am definitely NOT a scientific mind). let me know if that's something i do need to know about.

      in either case, THANK YOU so much for your insight! your info was/is super helpful!

    4. Regarding the hypotonic water, there was a claim somewhere in the Berkey website that it was advantageous to remove heavy metals while leaving smaller ions in the water, because hypotonic water (having less ions than the body) would leech important minerals from your body. I find that hard to swallow (no pun intended) because there are plenty of minerals in the foods we eat; I don't think water is the major source of our minerals. But that doesn't mean the purification system isn't still a good one.

    5. ah, ok. so not related to drinkability. good to know! thanks again for the info. this is really cool that you inform people like this!

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